The present invention relates to a method and apparatus for automatically adjusting a focal point of a taking lens in an apparatus such as a video camera or the like designed for reproducing continuously a state or behavior of an object.
The hitherto known methods of automatically adjusting a focal point of a taking lens (or automatic focusing) by detecting a distance to an object may be classified into an optical type and an ultrasonic type in accordance with the types of a media made use of in the measurement of the distance to the object, or alternatively they may be classified into an active type or a passive type in dependence on the types of processings of the media.
On the other hand, as the apparatus which incorporates a taking lens and in which the automatic focusing can be effectively adopted, there are known various types inclusive of still cameras, video or television cameras and others. In reality, the automatic focusing is practically applied.
In any type of the automatic focusing methods mentioned above, the distance measuring operation for deriving information or data of the distance to the object involves consumption of energy. Among others, the automatic focusing system of the active type requires a relatively great deal of energy for operation.
As to the energy consumption involved in the distance measuring operation, the apparatus in which the focusing has to be accomplished within an extremely short time as is the case in the still camera, i.e. the apparatus designed for reproducing only the instantaneous state or behavior of an object to be photographed is accompanied with no serious problem in connection with the energy consumption, since a single distance measuring operation is sufficient for the picture taking operation.
In contrast, in the case of an apparatus such as a video camera and the like which are intended for continuous reproduction of the state or behavior of an object, successive distance measuring operations for following up the object are required in taking picture of the object in motion. To this end, the distance measuring operation has heretofore been carried out successively and periodically at a predetermined time interval, thus involving an extremely large amount of energy consumption when compared with the distance measuring operation in the still camera and the like.